With the Michigan primary next month drawing increasing attention from the unannounced presidential candidates, television evangelist Marion G. (Pat) Robertson has joined Vice President Bush in forming a presidential exploratory committee to collect and spend money under the terms of federal election law.

Robertson's committee, Americans for Robertson, was organized with no fanfare on July 14, four days after Bush formed his "testing the waters" committee.

In a related development, Democrat James P. Keane, who is running against Rep. Jack Kemp (R) in his Buffalo congressional district, filed a complaint at the Federal Election Commission yesterday charging that the Michigan Opportunity Society (MOS) is an illegal front for Kemp's undeclared presidential campaign in that state.

The MOS, like the Bush and Robertson forces, has been recruiting candidates to run for precinct delegate in the Aug. 5 primary. The precinct delegates will play a critical role in the selection of the Michigan delegation to the 1988 GOP presidential convention, and MOS officials are closely tied to Kemp.

A Kemp spokesman dismissed the Keane complaint as "nonsense."

Robertson decided to set up an exploratory committee to ensure that all of his activities remain "above the letter and intent of the law," said Marc Nuttle, who runs Robertson's political action committee (PAC), the Committee for Freedom.

"People have been demanding to talk to Pat. If we spend any money to see them, that could be deemed testing the waters," Nuttle said. Formation of Americans for Robertson "keeps our books straight," he added.

So far, the Robertson campaign has been supported by a complex network of organizations. Foremost among these is the Freedom Council, a tax-exempt group that has recruited many of the candidates running for precinct delegate in Michigan.

Officials of the Freedom Council contend that their organization has no relationship to Robertson's presidential ambitions. The council accepts unlimited, tax-deductible donations from individuals and corporations, and does not disclose its activities.

In contrast, the Robertson backers' Committee for Freedom is a PAC that must report to the FEC. It can accept contributions of up to $5,000, but cannot be used to further his presidential bid.

Two other "draft Robertson" committees have registered with the FEC. These committees must operate independently, but they are allowed to accept and spend unlimited amounts on Robertson's behalf, according to preliminary FEC findings.

The newly formed group, Americans for Robertson, will be collecting money under the most restrictive of the FEC's regulations -- a $1,000 maximum from individuals -- and the funds will count against presidential primary spending limits, if he declares his candidacy.

Robertson backers say that an extensive recent Freedom Council mail survey of religious and conservative activists indicates a potentially strong base for him in Republican primaries and caucuses.

Of nearly one million recipients, just over 51,000 responded, and Robertson edged Bush, 27 percent to 25, with 14 percent for Kemp. Robertson supporters acknowledge that the survey was not scientific.